Saunders et al U.S. Pat. No. 4,063,064; Theeuwes et al U.S. Pat. No. 4,088,864; and Geerke et al U.S. Pat. 5,294,770 all disclose machines for transporting pharmaceutical tablets from a tablet reservoir to a laser treatment (ie, drilling) station where the tablets are treated (ie, drilled) by a laser. U.S. Pat. No. 5,294,770 additionally discloses laser drilling (ie, by burning) of multiple drug release ports in a single pharmaceutical tablet. Each delivery port is formed by a single pulse of a laser beam. Each port is formed independently of the other delivery ports on the tablet. Thus, the combined delivery port area of these multiple ports is simply the sum of the area of each of the ports. Since the area burned away by each laser pulse is dependent of the power of the laser pulse, the laser drilling of multiple ports requires proportionally more power.
In general the diameter of a laser drilled release port, such as disclosed in U.S. Pat. No. 5,019,397, is limited by the laser power available and the thickness and composition of the material being laser drilled. Osmotic drug dispensers typically have very thin (eg, less than 2 mm thickness) polymeric (eg, cellulose-based polymers) membrane walls. At present, most commercially sold lasers have a maximum power output of up to about 500 watts. Thus, a laser operating at 500 watts power output drilling through a cellulosic membrane having a thickness of only 0.1 mm can only drill an orifice having a diameter of up to about 0.7 mm. Unfortunately, dispensers are now being developed which require orifices having diameters of up to about 10 mm and even larger.